This invention relates to improvement in a gas storage canister, for example, using activated carbon or the like in order to treat fuel vapor of an automotive internal combustion engine.
In an automotive internal combustion engine for instance, a gas storage canister is provided to be able to store and release fuel vapor for the purpose of preventing fuel vapor generated in a fuel tank from releasing out of an automotive vehicle. Fuel vapor generated, for example, after a vehicle stopping is temporarily stored in the gas storage canister and is released together with fresh air from the gas storage canister to be introduced into the engine when the engine is operated after the vehicle stopping. Here, the following fact is known: In the gas storage canister using a gas adsorbing material such as activated carbon or the like, an exothermic reaction occurs when fuel vapor is adsorbed to the gas adsorbing material, so that the temperature of the gas adsorbing material rises. This temperature rise lowers a gas adsorbing ability of the gas adsorbing material. In contrast, an endothermic reaction occurs when fuel vapor is desorbed from the gas adsorbing material, so that the temperature of the gas adsorbing material lowers. This temperature drop lowers a gas desorbing ability of the gas adsorbing material.
In order to solve the above problems, Japanese Patent Provisional Publication No. 2001.248504 discloses a gas storage canister in which, in a casing, a gas adsorbing chamber is formed to be located at the side of one end wall provided with fuel vapor inlet and outlets while a heat accumulating and gas adsorbing chamber is formed to be located at the side of the other end wall provided with an atmospheric air communication opening. The gas adsorbing chamber is filled with a gas adsorbing material while the heat accumulating and gas adsorbing chamber is filled with a gas adsorbing material and a heat accumulative material.
Japanese Patent Provisional Publication No. 2001-145832 discloses a powdered heat accumulative agent which is produced by encapsulating a phase change material in micro-capsules which phase change material makes absorption and release of latent heat in accordance with a phase change. The powdered heat accumulative agent is uniformly mixed with powdered activated carbon (gas adsorbing material) and formed together with a binder into a certain shape, thereby obtaining a latent heat reservation type gas adsorbing material. Under the addition of the heat accumulative agent, a temperature change due to adsorption and desorption of fuel vapor may be suppressed to increase fuel vapor adsorbing and desorbing performances of the fuel gas adsorbing material.
Japanese Patent Provisional Publication No. 2003-311118 discloses a latent heat reservation type gas adsorbing material in which powdered heat accumulative material formed by micro-encapsulation similarly to in the above Japanese Patent Provisional Publication No. 2001-145832 is adhered to the surface of granular activated carbon having relatively large grain sizes.
However, the above conventional techniques have encountered in the following difficulties: In the technique of Japanese Patent Provisional Publication No. 2001-248504, the casing is formed into such a shape that heat absorption and release can be easily made, and a metal or the like having a higher specific heat is used as the heat accumulative material to soften the temperature change. However, there is a restriction for the shape of a layer of the gas adsorbing material while decreasing the amount of the gas adsorbing material to be filled in the casing.
In the technique of Japanese Patent Provisional Publication No. 2001-145832, if the latent heat reservation type gas adsorbing material is applied to a gas storage canister, the finely powdered gas adsorbing material is surrounded with the powdered heat accumulative agent having no gas adsorbing action, and therefore the adsorbing rate of gas may be lowered. Additionally, when a mixture of the powdered heat accumulative agent and the gas adsorbing material is formed together with the binder into the certain shape, it is required to accomplish the formation under a sufficient pressure in order to increase the adsorbing amount per unit volume. However, in case that the powdered heat accumulative agent and the gas adsorbing material are pressurized in a state where they are mixed, the micro-capsules are liable to be broken because the hardness of the outer shell of the micro-capsules formed of melamine or the like is low as compared with that of the powdered gas adsorbing material formed of activated carbon or the like so that the micro-capsules and the gas adsorbing material are largely different in hardness. In this regards, particular micro-capsules or particular forming methods are required. Thus, with usual micro-capsules and usual forming methods, the micro-capsules are liable to be broken, and therefore a desired heat reservation effect may not be obtained.
In the technique of Japanese Patent Provisional Publication No. 2003-311118, in case that the latent heat reservation type gas adsorbing material is applied to a gas storage canister, the surface of the activated carbon as the gas adsorbing material may be covered with the powdered heat accumulative agent having no gas adsorbing action. In such a situation, fuel vapor or the like to be adsorbed passes through the layer of the heat accumulative agent and reaches the gas adsorbing material, so that the adsorbing rate of fuel vapor is further lowered. Additionally, if the powdered heat accumulative agent is not fixed with a binder or the like in the gas storage canister, the powdered heat accumulative agent and the activated carbon will be gradually separated from each other within a casing under, for example, the repeated vibration applied during vehicle running.